1. Field of the Invention
The present invention relates to a frequency hopping communication device for performing spread spectrum communications while hopping between different frequency slots.
2. Description of the Prior Art
Frequency hopping is one method of spread spectrum communication and is well known in the art. In this method of communication, the carrier frequency is changed sequentially at every fixed interval according to a pattern indicating the order of frequency changes. This method is particularly good for handling interference and obstructed frequencies because, even if interference and the like are encountered on one frequency, the communicating device will hop to another frequency at which communication is possible. Further, the method is superior in maintaining privacy. By using a pseudo-random hopping pattern such as Reed-Solomon code, the method makes it difficult for a third party to intercept communication signals.
At the beginning of a communication session, the communicating devices must perform a synchronization acquisition operation to establish the same hopping pattern and synchronize the frequency used between the transmitter and receiver. More specifically, the receiver waits at a specific frequency slot until the transmitter hope to the same frequency slot and the receiver detects reception data transmitted from that transmitter.
However, this necessity for performing a synchronization acquisition operation at the beginning of a communication session in order to synchronize the hopping timing is, in fact, also a shortcoming of the frequency hopping method. If the period of the hopping pattern is relatively long, the receiver might have to wait a long time before the transmitter arrives at the same frequency slot. Hence, the conventional frequency hopping method requires much time to achieve acquisition at the beginning of a communication session.
Japanese Laid-Open Patent Publication (Kokai) No. HEI-8-191260, for example, describes a technology capable of rapidly achieving acquisition using a plurality of frequency synthesizers. However, providing a plurality of frequency synthesizers in the communicating devices also increases the size of the devices.